1. Field of the Invention
This application relates to a three-dimensional product having a nanoporous surface and a method for producing the same.
2. Description of the Related Art
A product which has a nanoporous surface, that is, indentations of nanometer-level (specifically a pore size of 1000 nm or less) on the surface, has electrical, optical and chemical properties that are different from those of a smooth surface and attracts attention as a functional material in various fields.
In fields such as agriculture and regenerative medicine, it is proposed that a product having a nanoporous surface be utilized as a cell culture scaffolding material for study and medical use (a scaffolding material in culturing cells) (refer to Japanese Patent Laid-Open No. 2001-157574 and Japanese Patent No. 4159103).
As a method for producing a product having a nanoporous surface, a fine pattern processing technique using electron beam exposure and X-ray exposure is considered. In addition, as a method for using a naturally formed structure, there is well known a method of using a nanoporous alumina anode oxidized film formed when aluminum is anode-oxidized in an acidic electrolyte (refer to Japanese Patent Laid-Open No. 11-200090).
However, a fine pattern processing technique requires a complicated processing using an exposure apparatus such as an electron beam exposure apparatus and an X-ray exposure apparatus. A nanoimprint technique employed for forming a nanoporous surface in Japanese Patent No. 4159103 is used for transferring a mold having a concave-convex structure of nanometer order to a product to be processed and requires precise condition controls such as transferring of the mold in the transferring process. In addition, the preparation cost of the mold is high and a mold having a large area is difficult to produce. Especially, as the cell culture scaffolding material, there are demanded a product in a three-dimensional shape which imitates biological organs and tissues and the like, in addition to a product in a planar shape, and fine pattern processing or nanoprinting is difficult to perform for a product having such a complicated three-dimensional shape.
Further, in order to efficiently culture cells, it is desired to set the density (porosity), pore size, pore size distribution and the like of the fine indentations on the surface of the cell scaffolding material in an appropriate range depending on the kinds of cells to be cultured, but in the method disclosed in Japanese Patent Laid-Open No. 2001-157574 or in the method of using an alumina anode oxidized film, the porosity, pore size or pore size distribution of the indentations are difficult to control.
For this reason, there has been demanded a method for producing a three-dimensional product having a nanoporous surface in which the pore density, pore size or pore size distribution can be easily controlled in a desired range.